:root {
  /* =========================
     COLORS
  ========================= */

  --color-bg: #2b2e33;
  --color-bg-soft: #34373d;

  --color-surface: #e9eae6;
  --color-ink: #23262b;
  --color-ink-soft: #6b6e73;
  --color-line: #d6d7d1;

  --color-screen: #1b1d1a;

  --color-digit: #ff8a3d;
  --color-blue: #6c8eff;
  --color-danger: #ff5c5c;

  /* =========================
     FONTS
  ========================= */

  --font-display: "Space Grotesk", sans-serif;
  --font-body: "Inter", sans-serif;
  --font-mono: "JetBrains Mono", monospace;

  /* =========================
     LAYOUT
  ========================= */

  --radius-card: 20px;
  --radius-control: 12px;

  --max-width: 470px;
}


/* =========================
   RESET
========================= */

* {
  box-sizing: border-box;
}


html {
  scroll-behavior: smooth;
}


body {
  margin: 0;
  min-height: 100vh;

  background: var(--color-bg);
  color: var(--color-surface);

  font-family: var(--font-body);

  display: flex;
  flex-direction: column;
}


/* =========================
   HEADER
========================= */

.site-header {
  width: 100%;
  max-width: var(--max-width);

  margin: 0 auto;

  padding: 32px 20px 18px;

  display: flex;
  align-items: center;
  gap: 14px;
}


.header-icon {
  width: 42px;
  height: 42px;

  border-radius: 12px;

  background: var(--color-digit);
  color: var(--color-ink);

  display: flex;
  align-items: center;
  justify-content: center;

  font-family: var(--font-mono);
  font-size: 20px;
  font-weight: 700;
}


.header-text h1 {
  margin: 0;

  font-family: var(--font-display);
  font-size: 30px;
  font-weight: 700;
  line-height: 1.1;
}


.header-text p {
  margin: 5px 0 0;

  color: #aeb1b6;

  font-size: 14px;
}


/* =========================
   MAIN
========================= */

main {
  width: 100%;
  max-width: var(--max-width);

  margin: 0 auto;

  padding: 0 20px 40px;

  flex: 1;
}


/* =========================
   TABS
========================= */

.calculator-tabs {
  width: 100%;

  display: grid;
  grid-template-columns: 1fr 1fr;

  gap: 8px;

  margin-bottom: 14px;

  padding: 5px;

  background: var(--color-bg-soft);

  border-radius: 14px;
}


.tab-button {
  height: 42px;

  border: none;
  border-radius: 10px;

  background: transparent;

  color: #aeb1b6;

  font-family: var(--font-body);
  font-size: 14px;
  font-weight: 600;

  cursor: pointer;

  transition:
    background 0.2s ease,
    color 0.2s ease,
    transform 0.1s ease;
}


.tab-button:hover {
  color: var(--color-surface);
}


.tab-button.active {
  background: var(--color-surface);
  color: var(--color-ink);
}


.tab-button:active {
  transform: scale(0.98);
}


/* =========================
   SECTIONS
========================= */

.calculator-section,
.age-calculator {
  width: 100%;
}


/* =====================================================
   AY ARITHMETIC CALCULATOR CSS
===================================================== */

.calculator {
  width: 100%;

  padding: 18px;

  background: var(--color-surface);

  border-radius: var(--radius-card);

  color: var(--color-ink);
}


/* =========================
   CALCULATOR DISPLAY
========================= */

.calculator-display {
  width: 100%;

  margin-bottom: 14px;
}


.calculator-display input {
  width: 100%;
  height: 105px;

  padding: 15px;

  border: none;
  border-radius: 14px;

  outline: none;

  background: var(--color-screen);

  color: var(--color-digit);

  font-family: var(--font-mono);
  font-size: 38px;
  font-weight: 700;

  text-align: right;
}


.calculator-buttons {
  display: grid;

  grid-template-columns: repeat(4, 1fr);

  gap: 10px;
}



.calculator-button {
  height: 64px;

  border: none;
  border-radius: var(--radius-control);

  background: #ffffff;

  color: var(--color-ink);

  font-family: var(--font-body);
  font-size: 20px;
  font-weight: 600;

  cursor: pointer;

  transition:
    transform 0.1s ease,
    opacity 0.2s ease,
    background 0.2s ease;
}


.calculator-button:hover {
  opacity: 0.82;
}


.calculator-button:active {
  transform: scale(0.95);
}



.number-button {
  background: #ffffff;

  color: var(--color-ink);
}



.operator-button {
  background: var(--color-bg);

  color: var(--color-digit);

  font-size: 23px;
}



.function-button {
  background: #d7d8d3;

  color: var(--color-ink);

  font-size: 18px;
}



.clear-button {
  background: #ffdede;

  color: var(--color-danger);

  font-weight: 700;
}



.equals-button {
  background: var(--color-digit);

  color: #ffffff;

  font-size: 23px;
  font-weight: 700;
}



.zero-button {
  grid-column: span 2;
}


/* =====================================================
   DAVID AGE CALCULATOR CSS
===================================================== */

.age-calculator {
  background: var(--color-surface);

  color: var(--color-ink);

  padding: 26px 20px 24px;

  border-radius: var(--radius-card);

  width: 100%;
}


.age-calculator h2 {
  margin: 0 0 8px;

  font-family: var(--font-display);

  font-size: 24px;

  font-weight: 700;
}


.age-description {
  margin: 0 0 22px;

  color: var(--color-ink-soft);

  font-size: 15px;

  line-height: 1.45;
}



.age-inputs {
  display: flex;

  flex-direction: column;

  gap: 16px;
}


.input-group {
  display: flex;

  flex-direction: column;

  gap: 7px;
}


.input-group label {
  color: var(--color-ink-soft);

  font-size: 14px;

  font-weight: 600;
}


.input-group input {
  width: 100%;
  height: 50px;

  padding: 0 14px;

  border: 1px solid var(--color-line);

  border-radius: var(--radius-control);

  background: #ffffff;

  color: var(--color-ink);

  font-family: var(--font-body);

  font-size: 16px;

  outline: none;

  transition:
    border-color 0.2s ease,
    box-shadow 0.2s ease;
}


.input-group input:focus {
  border-color: var(--color-blue);

  box-shadow:
    0 0 0 3px rgba(108, 142, 255, 0.15);
}


/* =========================
   CALCULATE AGE BUTTON
========================= */

.calculate-age-button {
  width: 100%;
  height: 48px;

  margin-top: 20px;

  border: none;

  border-radius: var(--radius-control);

  background: var(--color-ink);

  color: var(--color-digit);

  font-family: var(--font-body);

  font-size: 15px;

  font-weight: 700;

  cursor: pointer;

  transition:
    opacity 0.2s ease,
    transform 0.1s ease;
}


.calculate-age-button:hover {
  opacity: 0.9;
}


.calculate-age-button:active {
  transform: scale(0.98);
}


/* =========================
   AGE RESULTS
========================= */

.age-results {
  display: grid;

  grid-template-columns: repeat(3, 1fr);

  gap: 10px;

  margin-top: 22px;
}


.age-result {
  min-height: 92px;

  padding: 15px 8px;

  border-radius: var(--radius-control);

  background: var(--color-screen);

  display: flex;

  flex-direction: column;

  align-items: center;

  justify-content: center;

  text-align: center;
}


.age-result span {
  color: var(--color-blue);

  font-family: var(--font-mono);

  font-size: 32px;

  font-weight: 700;

  line-height: 1;
}


.age-result small {
  margin-top: 9px;

  color: #a5a7a3;

  font-size: 11px;

  font-weight: 600;

  letter-spacing: 0.5px;
}


/* =========================
   AGE SUMMARY
========================= */

.age-summary {
  margin: 16px 0 0;

  color: var(--color-ink-soft);

  font-size: 14px;

  line-height: 1.5;

  text-align: center;
}



.age-error {
  min-height: 18px;

  margin: 10px 0 0;

  color: var(--color-danger);

  font-size: 13px;

  font-weight: 600;

  text-align: center;
}



[hidden] {
  display: none !important;
}


/* =========================
   FOOTER
========================= */

footer {
  width: 100%;
  max-width: var(--max-width);

  margin: 0 auto;

  padding: 0 20px 30px;

  text-align: center;
}


footer p {
  margin: 0;

  color: #85888d;

  font-size: 12px;

  line-height: 1.5;
}


/* =========================
   TABLET
========================= */

@media (max-width: 600px) {

  .site-header {
    padding-top: 26px;
  }

  .header-text h1 {
    font-size: 27px;
  }

  .calculator {
    padding: 15px;
  }

  .calculator-button {
    height: 60px;
  }

  .calculator-display input {
    height: 95px;

    font-size: 34px;
  }
}


/* =========================
   MOBILE
========================= */

@media (max-width: 500px) {

  main {
    padding-left: 16px;
    padding-right: 16px;
  }

  .site-header {
    padding-left: 16px;
    padding-right: 16px;
  }

  .calculator-tabs {
    margin-bottom: 12px;
  }

  .tab-button {
    height: 40px;

    font-size: 13px;
  }


  /* Arithmetic Calculator */

  .calculator {
    padding: 13px;
  }

  .calculator-display input {
    height: 88px;

    padding: 12px;

    font-size: 30px;
  }

  .calculator-buttons {
    gap: 8px;
  }

  .calculator-button {
    height: 57px;

    border-radius: 10px;

    font-size: 18px;
  }

  .operator-button,
  .equals-button {
    font-size: 21px;
  }


  /* Age Calculator */

  .age-calculator {
    padding: 22px 16px;
  }

  .age-calculator h2 {
    font-size: 22px;
  }

  .age-description {
    font-size: 14px;
  }

  .age-result {
    min-height: 85px;
  }

  .age-result span {
    font-size: 27px;
  }

  .age-result small {
    font-size: 10px;
  }
}


/* =========================
   VERY SMALL SCREENS
========================= */

@media (max-width: 360px) {

  .calculator-button {
    height: 52px;

    font-size: 16px;
  }

  .calculator-display input {
    height: 80px;

    font-size: 27px;
  }

  .age-results {
    gap: 7px;
  }

  .age-result {
    min-height: 80px;

    padding: 10px 5px;
  }

  .age-result span {
    font-size: 24px;
  }
}